In some power management systems, power down should be controlled enough so the system can gracefully shut down. An example of such an application is the digital subscriber line or xDSL modem standards compliant applications, which require manufacturers to allow for a “dying gasp” time when input power is disconnected. Typically, this “dying gasp” is on the order of about 60 ms. During this “dying gasp,” xDSL modems can communicate with the central computer about the shutdown and allow for better traffic handling.
Conventional solutions generally employ large external capacitors to store enough energy to operate the xDSL modem for the “dying gasp” period. These capacitors are generally on the order of 2000 μF to 8000 μF. Because these are large external capacitors, they are bulky and expensive, so it is desirable to reduce their size to produce a more economical xDSL modem.
Additionally, an example of conventional circuits is U.S. Pat. No. 7,098,557.